The long term objective of this research is to characterize the sexual development of the filamentous fungi at the molecular level. Although these organisms are of vast economic and social importance, very little is known of their development. The much-studied bread mold Neurospora crassa will be used as the model organism. Neurospora undergoes a complex process of sexual differentiation; a number of the regulatory and target (mating-specific) genes that are involved in this process have already been identified. The structures and functions of these genes will be examined, as will the control of their expression and the interactions between their gene products. The roles of the mating-specific genes in sexual development will be determined using a reverse-genetic approach, and the phenotypes observed when these genes are dysfunctional will be characterized microscopically. The evolutionary conservation of the mating-specific genes will be examined. The factors that cause these genes to be expressed specifically during sexual development will be studied; in preliminary experiments, three control pathways were identified. The interactions between these control pathways will be examined, and a search for other elements involved in the control of gene expression during sexual development will be executed. The structures (nucleotide sequences) of a regular gene (fmf-1) and selected mating-specific target genes will be determined, and the properties of their encoded products examined. An in vitro analysis of the regulatory elements recognized during sexual development will be carried out using mobility shift assays and DNA footprinting experiments; this analysis will serve to identify important control elements and further define the roles played by the regulatory gene products. Finally, the hierarchy of events required for normal sexual development in Neurospora will be examined, by determining the effects of selected processes on the overall sexual developmental pathway. Some filamentous fungi are exploited for the production of useful compounds, but others cause devastating diseases. Basic information about the control of their life processes will allow judicious use of the beneficial fungi, and will also further efforts to control the pathogens.